The present invention relates to the field of electronic circuits, and, more particularly, to a tester and method for testing electrical parameters of circuit paths including at least one electronic circuit device.
Integrated circuits (ICs) are well known and are used in a variety of telecommunications, computer, and other electronic devices. It is important to detect defects and/or design limitations of such integrated circuits during their design and testing phase. This is so that these problems may be corrected before large scale manufacturing takes place. Furthermore, is may also be important to monitor electrical properties or parameters of such ICs over their lifetime to detect problems that may arise in certain applications so that these problems may be corrected in future designs.
One method for testing ICs for latent defects or other problems is stress testing. Stress testing involves applying a stress voltage to an integrated circuit and measuring the effects that the stress voltage has on certain electrical parameters. For example, the stress voltage may be used to accelerate degradation of semiconductor device layers due to hot carrier injection. The effects of such hot carrier degradation or aging may then be determined using parametric analyzers or other measurement devices, as will be appreciated by those of skill in the art.
One example of a stress tester is disclosed in an article entitled xe2x80x9cNovel Self-Stressing Test Structures for Realistic High-Frequency Reliability Characterizationxe2x80x9d by Snyder et al., 1993 IEEE Intl. Reliability Physics Symposium Proceedings, pp. 57-65. The article discloses a self-stressing test structure that may be used for reliability failure measurements caused by hot carriers, electromigration, and oxide breakdown, for example. The test structure includes a high-frequency on-chip oscillator having a frequency controlled by an external DC voltage. A high frequency, oscillating (i.e., an alternating current (AC)) test signal is produced thereby and may be routed to various circuit elements. The test signal may be electronically isolated to allow DC measurement of the various circuit elements.
While the above AC self-stressing test structure may be useful for determining the effects of high frequency operation on an integrated circuit, other factors may also effect electrical parameters. For example, overshoots or undershoots of an input voltage to a circuit may also cause hot carrier injection or other problems independent of operating frequencies. Additionally, it may be desirable to measure the effects of voltage overshoots or undershoots, for example, over a circuit path including a plurality of circuit devices rather than on a single device.
In view of the foregoing background, it is therefore an object of the invention to provide a tester and related methods for testing a circuit path which tests not only the effects of high frequency operation but also the effects of voltage overshoots and undershoots.
This and other objects, features, and advantages in accordance with the present invention are provided by a tester for a circuit path including a voltage controlled oscillator (VCO) for generating a controllable frequency oscillating test signal and having a controllable amplitude defined between first and second voltages, a multiplexer for selectively connecting one of the oscillating test signal, the first voltage, and the second voltage to the circuit path, and a selector for selectively connecting the multiplexer to the circuit path. Moreover, at least one of the first and second voltages may be controllable so that the VCO generates the oscillating test signal to selectively have one of an amplitude greater than, less than, and equal to an amplitude of an output of the circuit path. The circuit path may include a plurality of electronic circuit devices connected together.
More particularly, the circuit path, the VCO, the multiplexer, and the selector may be integrated on a circuit chip. Additionally, the VCO, the multiplexer, and the selector may be fabricated using complementary metal oxide semiconductor (CMOS) components. The plurality of electronic circuit devices may be at least one of analog circuit devices, digital circuit devices, and mixed signal devices. Furthermore, the VCO may control the frequency of the oscillating test signal based upon one of the first and second voltages.
A method for testing a circuit path according to the invention includes generating first and second voltages, generating a controllable frequency oscillating test signal having a controllable amplitude defined between the first and second voltages using a voltage controlled oscillator (VCO), and selectively connecting one of the oscillating test signal, the first voltage, and the second voltage to the circuit path. At least one of the first and second voltages may be controlled so that the VCO generates the oscillating test signal to selectively have one of an amplitude greater than, less than, and equal to an amplitude of an output of the circuit path. Also, the circuit path may include a plurality of electronic circuit devices connected together.
Moreover, the method may also include measuring at least one electrical parameter of the circuit path. Measuring may include measuring the at least one parameter using a parametric analyzer. Additionally, the at least one electrical parameter may include at least one of transconductance, maximum current drive, and threshold voltage. The method may also include disconnecting the oscillating test signal, the first voltage, and the second voltage from the circuit path prior to measuring. Furthermore, the method may include controlling the frequency of the oscillating test signal based upon one of the first and second voltages.